Visual Studio Builds: Build gdkmm into gtkmm
Hi,
Lately GTKMM master has been updated to be like GTK master where GDK(mm) is no longer built as a standalone library but is instead made a part of GTK(mm). This MR attempts to update the Visual Studio builds to do likewise.
Also remove all traces of gdkmm.rc, since that is no longer used.
With blessings, thank you!